Some of the toughest environments for protective coatings to withstand are seen in the power industry, particularly within the flue gas desulfurization (FGD) process. Temperatures within the different areas throughout the system may reach 350-450°F (177-232°C) and then be cooled to ambient temperatures upon shutdown of the unit. The cooling causes oxidized sulphur to condense with the moisture forming sulphuric acid. This heating and cooling puts tremendous stress on the lining as it shrinks and expands combined with post cure stresses. The lining also undergoes attack by sulphuric acid which can react with the lining, basically dissolving it from the substrate. In this environment, a lining’s cross-link density is critical to the survival in this harsh environment.

Selecting the right lining chemistry can be difficult due to all the performance attributes that must be considered when approaching the aggressive environments of FGD applications. Vinyl esters generally appear to perform better than epoxies given similar cure conditions with regard to temperature and time. The following paper will provide insight into some of the fundamental differences between these lining chemistries and how they contribute to their performance in FGD applications. There are many differences between fillers, binders, promoters, and other modifiers, but the main focus of this paper is the mechanism of cure of the different polymer binders - chain growth versus step growth.

The chain growth mechanism of the vinyl ester / peroxide responds differently to post cure stress than the step growth mechanism of the epoxy / amine system. Data discussed here shows the rate differences of post-cure of the peroxide radical / vinyl esters when compared to the epoxy systems. Also presented, are the differences in achievable molecular weight and control by different peroxide levels. The correlation of sulphuric acid immersion and dry heat exposure data to the cross-linking mechanism of the lining is discussed along with how it relates to internal and independent laboratory testing.

Subject
Acids, Coatings, Vinyl ester, Sulfuric acid, Flue gas desulfurization, Molecular weight, Novolacs, Polymers, Heat, Coal, Immersion, Epoxies, Lining
© 2012 Association for Materials Protection and Performance (AMPP). All rights reserved. This work is protected by both domestic and international copyright laws. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2012
Association for Materials Protection and Performance (AMPP)
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